“Yet even so the best part of a hundred years after the Doom of Valyria (the rightly named Century of Blood), House Targaryen looked east, not west, and took little interest in the affairs of Westeros, Gaemon Targaryen, brother and husband to Daenys the Dreamer, followed Aenar the Exile as Lord of Dragonstone, and became known as Gaemon the Glorious. Gaemon’s son Aegon and his daughter Elaena ruled together after his death. After him Lordship passed to their son Maegon, his brother Aerys, and Aerys’s sons, Aelyx, Baelon, and Daemion. The last of the three brothers was Daemion, whose son Aerion then succeeded to Dragonstone.” - Fire and Blood.
Before conquest family tree 😄 more like family wreath 😨.
“The tradition amongst the Targaryen had always been to marry kin to kin. Wedding brother to sister was thought to be ideal. Failing that, an uncle, a cousin, or a nephew, a boy a cousin, aunt, or niece. The practice went back to Old Valyria, where it was common amongst many of the ancient families, particularly those who bred and rode dragons. The blood of the dragon must remain pure, the wisdom went. Some of the sorcerer princes also took more than one wife when it pleased them, though it was less common than incestuous marriage.” - Fire and Blood.